It is often necessary for construction workers, repairmen, fire fighters, and maintenance workers to move safely across a sloping surface such as a roof which may not offer a user sufficient friction for safe maneuvering, or which may not be uniformly able to support the weight of the person. In such cases, something is needed to assist the person. Ladders having hooks which engage the ridge of a roof and thus prevent sliding are known and are described in U.S. Pat. Nos. 599,963, 4,184,569, and 4,311,207, for example. These ladders provide sufficient safety, but are not useable where a roof ridge is unavailable. Requiring the user to contact the ridge line in order to engage the hooks may be difficult for a very large roof or impossible in the case of a sloping roof which meets a vertical wall at its upper edge.